Effects of aluminum in the sludge of Saydabad water treatment plant on environment

Abstract

Sayedabad water treatment plant was established in 2002 to serve water demand of Dhaka city. Large scale use of aluminum in coagulation process during water treatment in Sayedabad Water Treatment Plant may generate significant quantities of aluminum rich treatment sludge and disposal of this sludge may lead to environmental pollution. The common practice is open water disposal or on land disposal. Aluminum leaching from such sludge may pose potential threat to both groundwater and surface water with long-term consequences. In this study, water quality in supernatant of excess alum sludge in receiving water bodies have been assessed. Besides, the leaching characteristics of aluminum sludge have been evaluated with a view to assessing the effects of aluminum sludge on environment. This study has also attempted to assess the uptake of aluminum from sludge by red amaranth plants. . The water quality parameters suggest that there is no significant impact on surface water due to disposal of supernatant of alum sludge. The spatial variation of AI concentration indicates there is little variation of aluminum (AI) concentration distribution at varying distances from the point of discharge. The leachate concentration can be significant enough to percolate through alum sludge into groundwater. This percolated leachate concentration might raise the concentration of Al in groundwater above the allowable limit as suggested by World Health Organization guideline value and Bangladesh standard for drinking water. The leachate from column leaching test indicates that distilled water and chloride have the highest tendency to leach Al from sludge. Significant amount of AI could be leached from alum sludge by distilled water, chloride, sulfate, nitrate and hydroxide anions. The leachate from chloride anion fluid media is higher than distilled water, nitrate, sulfate and hydroxide anion fluid media. Aluminum uptake from sludge by red amaranth plants has been studied and it has been found that the red amaranth phmts accumulate AI from soil and the concentration varies among the different parts of plants. Roots of red amaranth accumulated the highest concentration followed by stems and leaves. The 'quantity of accumulated AI decreases from roots to leaves gradually. The mean AI concentration in leaves is 2.4 times less than stem and 4.1 times less than root. The Al concentration of red amaranth plants grown in Al sludge was 451 ppm, which is about 3 times higher than the AI concentration of red amaranth plants grown in AI sludge free soil.